Users can provide inputs to electronic devices using many different approaches. For example, an electronic device can include different input interfaces by which a user can interact with the device. The input interfaces can include, for example, one or more switches, buttons, actuators, or sensors (e.g., touch sensors), the actuation of which the device can detect. In some cases, an electronic device can include a dome switch, which can be depressed to provide a detectable input. The dome switch is typically constructed by placing a conductive dome over a contact pad on a circuit board. When the dome is pressed, the dome can invert such that an inner surface of the dome contacts the contact pad. The dome inversion also provides a tactile ‘click’ that enhances the user's interaction with the switch. To actuate the dome switch, a user typically presses a cosmetic piece placed over the dome. In response to the user pressing the cosmetic piece, the dome is in turn is depressed and comes into contact with the contact point.
A dome switch can enclose a volume of air between the inner surface of the dome and the circuit board to which the dome is mounted. When the dome is depressed, the air within the enclosed volume may need to be displaced so that the center of the dome can contact the circuit board contact pad. To displace the air, a coversheet placed over the dome can include openings connecting the interior volume to the environment in which the dome switch is placed. When the dome is collapsed to close a circuit, air can be expelled from the internal volume through the openings, and remove an air pressure resistance to the dome movement. Air can re-enter the internal volume through the openings when the dome reverts to its initial position.
The openings in the dome coversheet, however, can provide a path for debris, water, or other external particles to enter the internal volume of the dome switch. If a conductive particle infiltrates the internal volume, the particle can cause corrosion or promote the formation of substances that prevent the proper operation of the switch. For example, particles can cause rust, oxidation, dendrite growth, or salt, sugar or chemical deposits. As another example, water can infiltrate the internal volume of the dome switch and short the switch.